The mechanism of gene regulation at the molecular level will be studied with special emphasis on the role of DNA properties as a determinant of specificity. One objective of this project is to identify and characterize the dynamic structure of procaryotic double-stranded DNAs with the goal of determining the correlation between DNA physical properties and gene regulation. High resolution thermal denaturation studies and other physical and biological determinations will be performed on DNAs with established sequences including procaryotic viral DNAs, highly purified DNA restriction fragments containing known genetic loci, mutant DNAs with known phenotypes and sequence changes, and DNA model polymers. The DNA restriction fragments will be purified by high pressure RPC-5 column chromatography and/or by gene cloning. Studies will be concentrated on regulatory sites containing operators and promoters with established nucleotide sequences. A second objective is to identify and characterize the extent and type of helical structure in the "single-stranded" viral DNAs from bacteriophages phi X174 and M13 and related viruses. The relationship of this helical structure to their biological functions, such as replication and packaging in the phage particle, will be explored. Also, the use of certain DNA restriction endonucleases as probes of helical structure will be investigated further.